H robertson



Jan. 31,1956 H, ROBERTSON 2,733,376

ELECTRODE SUPPORT FOR ELECTRON DISCHARGE DEVICE Filed Feb. 27, 1952 2 Sheets-Sheet l l F/G.

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lNl ENTOR G. H. ROBERTSON A TTORNEY Jan. 31, 1956 ROBERTSON 2,733,376

ELECTRODE SUPPORT FOR ELECTRON DISCHARGE DEVICE Filed Feb. 27, 1952 2 SheetsSheet 2 M/VENTOR 61H. ROBERTSON A 7' TORNEV wane.

2,733,376 Patented Jan. 31, 1956 ELECTRODE SUPPORT FOR ELECTRON DISHARGE DEVICE George H; Robertson, Summit, N. 5., assignor to Bell Telephone Laboratories, incorporated, New York, N.,Y., a corporation of New York Application February 27, 1952, Serial No. 273,645 11 Claims. (Cl. 313-261) This invention relates to electron discharge devices and, more particularly, to such devices having close interelectrode spacing.

Itis known in the art that the specific dimensions and electrode spacing of an electron discharge device may be determined to provide prescribed values of the arm plification factor, the plate resistance, and the transconductance. When the electrode spacings determined are small, for example a control grid-cathode spacing of the order of inch, the problems of designing such a structure which may be easily reproduceable to precise tolerances are greatly magnified. Inaddition to the requisite tolerances, it is also of prime importance in closespaced electron discharge devices having planar electrodes that the entire surfaces be at the prescribed spacing and not merely that the average spacing be correct. The latter situation exists When the surfaces are not exactly parallel. With a control grid-cathode spacing of the magnitude mentioned above, a change in the spacingor a variation in the spacing of different areas of the electrodes of of an inch is extremely slight in absolute magnitude but may cause a pronounced reduction in the transconductance of the device and consequently a failure to meet the requisite performance characteristics.

These problems, which are inherent in the manufacture of devices with such critical spacing, are aggravated by the fact that mica, the usual insulating material employed in electrode structures, is unsuitable in these applications. .The usual practice in electrode mount construction is to employ a pair of spaced mica discs with punched openings into which the electrodes are inserted with the'electrode spacing'determined by the distance between the edges of the openings. Since the punched openings in the mica members determining the electrode spacing have irregular edges, the electrode spacing amounts to only an approximation of the desired value which is not suflicient to meet, the tolerance requirements for high quality performance and reproducibility. Also the mica in intimate contact with the cathode and anode at elevated temperatures tends to give off water and volatile impurities, the presence of which is undesirable in the atmosphere. of the device, and which leaves the mica at reduced strength.

For these and other reasons, it is desirable to provide an electrode structure employing stable insulating materials having a comparatively low coetficient of thermal expansion and being capable of accurate manufacture as by grinding.

As disclosed in the application, Serial No. 231,816 filed June 15, 1951, of C. T. Goddard, now issued as Patent No. 2,663,819, a single-sided electrode structure having close, accurate electrode spacing may be constructed. In the interest of heater power economy, however, it is desirable to provide a structure which is suitable for double-sided planar electrodes while maintaining' both sides of the electrodes accurately spaced.

I One general object of this invention is to improve the 2 structure of electron discharge devices having close spaced electrodes. r

More specifically, objects of this invention are to facilitate the attainment of prescribed electrode spacings in and performance characteristics.

In one illustrative embodiment of this invention, an electron discharge device comprises a cathode having compassing the grid.

In accordance with one feature of this invention, the cathode and grid are mounted in prescribed relation to grid portions.

In accordance with another feature of this invention, the cathode and grid and the mounting elements therefor pansion and contraction of the electrodes with temperature variations but without substantial alteration in the spacing between each emissive surface and the grid portion in juxtaposition thereto.

Inone specific embodiment, an electron discharge device comprises a series of spaced parallel conducting fact with a cathode at the ends of the structure. Two

cathode surfaces are located between the parallel rods with their emissive surfaces in close proximity to the control electrode Wires. The cathode surfaces are fastened to the insulating bars and rest against the projections in a manner so that the height of the projections determines the spacing between the cathode surface and the control electrode.

A more complete understanding of these and other features of this invention may be had from the following detailed description with reference to the accompanying drawings in which:

Fig. 1 is a view in perspective of an electron discharge device incorporating 'an electrode structure in accordance with this invention, portions of the envelope and structural members being broken away to show details clearly;

Fig. 2 is a plan view of the electrode structure of the device shown in Fig. .1 with the envelope and certain connections in cross section; i

Fig. 3 is a cross section of the electrode structure along plane 3-3 of Fig. 2;

Fig. 4 is a perspective view of a portion of an electrode structure employing this invention similar to the structure shown in Figs. 1, 2, and 3 but having a different arrangement of edge projections on the insulating bars;

Fig. 5 is a fragmentary sectional view of the step-and cathode support details of the device as shown in Fig. 4.

minal pins. Two pairs of spaced insulating bars 13 are mechanically'biased against the parallel side rods 12, one pair on each side of the side rods 12 and opposite the other pair. The insulating bars may be made of corundum, fused quartz or other ceramic having the physical properties of thermal stability-withrespect to expansion, conductivity and volatility, as well as being readily machinable. The'bars 13 are affixed to the side rods 12 by spring or resilient clips 14-, one end of which is attached, as by welding, to a side rod. 12 and the other end of which is located in notches 15 in an edge of the bars 13 to prevent their lateral movement. Each of the bars 13 has an accurately ground plane surface 16 tangent to the side rods 12 and defining a plane therewith. Between the side rods 12 is an edge projection 17 on each of the bars 13, the purpose for which will hereinafter be explained.

A tubular metal anode 21 of rectangular cross section surrounds and is atfixed, as by welding, to both side rods 12. i v

Coplanar with side rods 12 are two pairs of parallel metal rods, screen grid support rods 22, and control grid support rods 23. The bars 13 are clipped to support rods 22 and 23 in the same fashion as they are affixed to side rods 12. A screen grid 24, comprising a rigid wire in a rectangular helix with its axis parallel to the support rods 22, is affixed to those rods.

The second pair of support rods, to wit,'rods 23, is also coplanar with side rods 12 and located between rods 22. Rods 23 are maintained rigidly parallel to each other by a pair of straps 25 which are welded to each side forming a ladder-like structure. Between the pairs of straps 25 is a control grid 26 comprising a fine tungsten wire tautly wound on support rods 23 coplanar with the surfaces 16 of bars 13. The control grid wires are of the order of 0.0603 inch in diameter and are covered with a thincoating of gold to inhibit grid emission. Locatedbetween the grid wire parts 27 each of which has an emissive coating of barium, strontium and calcium carbonates adjacent the control grid 26. The cathode parts 27 of nickel are channel shaped and are positioned in opposed nested relation. A cathode heater 2%, only the leads 29 for which appear in this figure, is located in the enclosure formed by the cathode parts 27. Each of the cathode parts 27 is biased individually against the edge projections 17 of the bars 13 so that the grid-cathode spacing is equal to the height of the projection 17, in this specific embodiment, @4 of an inch. 7 Resilient metal clips 31 mechanically bias the cath-, ode parts 27 against the bars 13 and lateral movement of the cathode members may be prevented by notches ,in those parts of cathode members 27 where the clips 31 rest, as well as by additional notches in the bars 13 similar to the notches 15. e

Electrical connections to the cathode members 27 comprise flexible strips 32 of metal, such as nilvar, one for each cathode member, which are connected to one of the terminal pins 11. The electrical connections for the cathode heater 28 comprise leads 29 which are afiixed to additional terminal pins 11. Anode 21 is electrically connected to side rods 12 which are rigidly affixed, as by welding, to two oppositely located terminal pins 11 forming both the electrical connection for the anode 21 and support for the entire electrode structure. The screen grid 24 is electrically biased through a flexible nickel strap 33, one end of which is welded to one screen grid support rod 22 and the other end of which is welded to another terminal pin 11. The control grid 26 is biased electrically in a similar manner, that is, by way of a flexible nickel connector 34, one end of which is welded to a control grid supportrod 23 and the other end of which is welded to a terminal pin 11'. v

A getter plate 35 extends above the electrode structure and is welded'to metal getter support rod 36 which is in turn welded to a side rod 12.

The details of the electrode structure and particularly planes are two cathode V the cathode support arrangement may be more clearly seen by reference to Fig 2. The insulating bars 13 are supported by rods 12 22 and 23 with the plane surface 16 of each lateral bar 13 tangent to each of the rods thereby defining two parallel reference planes. Screen grid support rods 22 and control grid support rods 23 are the same diameter as side rods 12 and maintain the parallelism of the reference'planes. The anode 21 and the screen grid 24 are rectangular in'shape and are tangent to the side rods 12 and screen grid support rods 22, respectively. Each of these electrodes is attached to its support rod at the point of tangency.

The channel-shaped cathode parts 27 are mechanically biased by bent metal clips 31 against the edge projections 17 of the bars 13. The edge projections 17 each have :1 planar and surface which is ground parallel to the plane surfaces 16 of bars 13 thereby defining a second pair of reference planes which are both parallel to the first reference planes formed by the plane surfaces 16 resting upon the rods 1 22 and 23. The emissive surfaces of the cathode parts 27 are coplanar with the reference plane defined by the edge projections 17 The grid-cathode spacing for each side of the double-sided structure depends upon the distance between the two reference planes as determined by the height of the edge projections 17 which extend nearly across the outer faces of the cathode parts 27 to provide ample support for the cathode and to insure that the entire area of the grid and cathode surfaces remain at the predetermined distance apart despite thermal changes in the size of the structure. The channehshaped cathode parts 27 are interleaved so as to form a closed chamber for the cathode heater 28 while allowing each to expand separately without any bowing of the planar emissive surfaces which would tend to vary the grid-cathode spacing from the predetermined value. 7

The cathode support and the nature of the edge projection 17 may also be clearly seen in Fig. 3. One end of bent metal clips 31 is located in notches 15 as are spring clips 14, but the end of bent metal clips 31 adjacent the cathode members 27 has a right angle bend which fits through a notch and over the end of the cathode members 27 rigidly holding each to its respective bar 13. Between the bars 13 are the straps 25 which make up a rigid control grid structure with the control grid support rods 23. The control grid 26 is wound laterally under tension on its support rods 23 forming two parallel surfaces which are coplanar with the reference planes formed by the plane surface 16 of the bars 13. A suitable method of manufacture for the control grid is disclosed in E. J. Walsh Patents 2,549,551 granted April 17, 1951, and 2,567,415 granted September 11, 1951.

The electrode structure comprises an integral unit built around the framework of the side rods 12 and the insulating bars 13. The electrode spacings are all determined by the members contained within the framework and not dependent upon any contact with the envelope 10 or other members. The side rods 12 are aifixed as by welding to a pair of oppositely located terminal pins and form the sole support for the electrode structure. Connections to the cathode parts and the grids are made by flexible'metal straps so that there is no normal force acting upon the support rods which would tend to destroy the parallelism of the surfaces 16. The electrode structure determines the spacing of the electrodes by means of reference planes determined by planar surfaces tangent to round support rods of uniform diameter. Both the diameter of the metal rods 12, 22 and 23 and the surface 16 are subject to manufacturing tolerances far closer than -is possible with perforated mica discs, but the extreme accuracy lies in the fact that a single dimension, the height of the edge projection 17 above the plane surface 16, determines the grid-cathode spacing. There are no additive tolerances which introduce a greater opportunity for variations in spacing. Also, uniformity of spacing throughout the entire surface of the cathode members electrode spacing which is determined by the distance between parallel reference planes. Substantially all of the thermal expansion of the members in a direction normal to the planes does not affect the interplanar distance. This distance is determined by the height of the edge projection 17 on bars 13, and expansion of either the bars 13 or the cathode parts 27 will not affect the spacing. The electrode structure is held together by expandable clips 31 which bias the cathode parts 27 to the edge projection 17 but will allow for expansion of either of those members in the normal direction Without disturbing the electrode spacing. Each of the cathode parts 27 is supported independently of the other so that there is no tendency to bend or break due to uneven expansion, as would be the case if the cathode were a single piece. Consequently, each of the cathode parts 27 is free to expand in a direction parallel to the reference planes but deleterious movement of those members may be prevented by having clips 31 rest in notches in the ends of the cathode parts as shown in Fig. 5. The interlocking arrangement of the channel-shaped cathode parts provides a substantially closed container for the cathode heater in the interest of heater power economy, but expansion of the members will not affect the gridcathode spacing.

The planar surfaces which determine the electrode reference planes are a part of the unitary bar 13, so that the critical dimension, to wit, the height of the edge projection, determines the accuracy of the electrode spacing of the device. Particularly desirable ceramics for the bars 13 are corundum, also known as synthetic sapphire, and fused quartz, for thesematerials may be subjected .to accurate grinding and neither of them contain volatile impurities as may be the case with mica. Also, there is more freedom in the design of members made from corundum or fused quartz which is readily grindable than there is with mica which is laminar and not accurately grindable. The bars 13 may be ground from a single piece of the above-named materials or the planar space 16 may be ground and then a plate of the same material may be fused to a side of the bar by the application of concentrated heat to the members away from the planar space. Then the height of the edge projection 17 may be determined by reference to the surface 16 and ground accordingly.

An alternative arrangement of steps or projections on the insulating bar 13 is shown in Fig. 4 and Fig. 5. Three steps 41, running parallel to the length of cathode parts 27, are located on the insulating bar 13 rather than the overhanging projection 17 shown in Figs. 1, 2 and. 3. The three-step arrangement shown in Fig. 4 is readily adaptable to the manufacture of each of the bars 13 from a single piece of suitable insulating material.

It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Modifications may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. An electrode structure for an electron discharge device comprising a pair of spaced parallel rods, insulating bars on opposite sides of said rods adjacent the ends thereof and extending between said rods, said bars and said rods defining two parallel planes therebetween, a control electrode mounted by said rods and having major portions lying in said planes, said bars having portions defining two additional parallel planes, each adjacent a respective one of said first planes, and an electron emitting 6 electrode positioned against certain of said portionslof said insulating bars having a portion in each of said additional parallel planes, said bars lying beyond said major portions of said control electrode. 7

2. An electrode support structure for an electron discharge device comprising a pair of parallel metal rods, a pair of spaced insulating bars affixed to each side of thereto, an inwardly extending projection on each of said insulating bars, a control electrode mounted on said rods and having a pair of faces each coplanar with the respective tangent surfaces of said insulating bars, and an electron emitting electrode having two faces each parallel to a respective face of said control electrode and positioned by said projections.

3. An electrode structure for an electron discharge device comprising a plurality of spaced rods, a series of planar insulating bars mounted in fixed transverse relation to said rods, each of said insulating bars having an inwardly projecting portion, a double-sided planar electron emitting electrode with emissive surfaces upon each side mounted against the projecting portions of said inportion of said insulating bars.

4. An electrode structure for an electron discharge device comprising a pair of parallel rods, a double-sided planar cathode member between said rods, a control electrode tangent to each side of said rods and extending therebetween, and means mounting each of the sides of said cathode member independently at a predetermined distance from said control electrode, said means comprising a pair of insulating bars on each side of said rods, each of said insulating bars having a planar surface coplanar with said control electrode and a projection on each of said insulating bars adjacent said cathode member.

5. An electrode structure for an electron discharge device comprising a pair of spaced support rods, 21 series of bars mounted against said rods and defining a first pair of parallel planes therewith, one plane on each side of said rods and tangent thereto, a grid wound about said rods the ends of said cathode.

6. An electrode structure in accordance with claim 5 wherein each of said bars has a planar surface mounted tangent to said rods to define said parallel planes and said spring means bias each of said surfaces against said rods.

7. An electrode structure for'an electron discharge device comprising a pair of spaced rods, a series of insulating bars extending between said rods and defining a pair of first parallel planes therewith, each of said bars having a plurality of steps extending inwardly between said rods, the steps defining a second pair of parallel planes, a cathode member having emissive surfaces thereon, a control electrode having portions in said first planes, and a series of resilient clips mounting each of said emissive surfaces against said steps of the insulating bars.

8. An electrode structure in accordance with claim 7 wherein said resilient clips mount each of said emissive surfaces against the steps of the insulating bars independent of the other of said emissive surfaces.

9. An electrode structure in accordance with claim 7 wherein said cathode member comprises a pair of channelshaped parts in opposed nested relation, each of said parts mounted individually against the steps of said bars, whereby thermal expansion of either of said parts does not affect the position of the other part.

.10. An electrode structure for an electron discharge device comprising a pair, of spaced parallel rods, a control electrode wound about a central portion of said rods in a series of lateral turns, spacer members on each side andadjacent the ends of saidrods, said spacer members each having a pair of parallel planar surfaces, the first of said pair of surfaces mounted against one side of both of said rods, the second of said pair of surfaces disposed between said rods, an electron emitting electrode within said control electrode, means mechanically biasing said electron emitting electrode against the second of said surfaces, and. means mechanically biasing said spacer members against said rods.

11. An electrode structure for an electron discharge device comprising a pair of parallel support rods, two pairs 1- of insulating bars extending between said rods, each pair being adjacent a respective end of said rods and said rods being positioned between said pairs of bars, said bars having surfaces defining'a first pair of parallel planes and having also projections defining a second pair of planes between saidfirst planes and parallelthereto, said surfaces being tangent to said rods, a cathode having two planar emissive members each positionedin a respective one of said second planes, a helical grid mounted by said rods and having two planar portions each positioned in a respective one of said first planes, resilient means urging said bars against said rods, and resilient means urging said emissive members against said projections.

References Cited in the file of this patent UNITED STATES PATENTS 2,091,047 Kauffeldt Aug. 24, 1937 2,310,662 Vogel Feb. 9, 1943 2,459,476 Van Liempt Jan. 18, 1949 

